On Mon, 25 Jun 2007, Hugh Dickins wrote: > > In many situations the page struct passed to flush_dcache_page is > > simply used to calculate the virtual address. So its mostly harmless. > > Trouble starts when page attributes like the mapping is used. > > Mostly harmless indeed. I don't understand why you insist on trying > to complicate the situation. flush_dcache_page is only expected to > do something on pages mapped into userspace (correct me if I'm wrong > there), it's expected to do nothing on kmalloc'ed pages. It's > been working that way for years, and will continue to work that way > with slub, providing either page_mapping or flush_dcache_page checks > PageSlab to avoid oopsing on page->mapping.
It is definitely intended to work. Otherwise we would not have code like this: [EMAIL PROTECTED]:~/linux-2.6$ find . -name "*.c" | xargs grep "flush_dcache_page"|grep virt ./drivers/scsi/scsi_tgt_if.c: flush_dcache_page(virt_to_page(ev)); ./drivers/scsi/scsi_tgt_if.c: flush_dcache_page(virt_to_page(ev)); > 2.6.22-rc6 has page_mapping making that check: we could argue about > which is the better site for it, there are good arguments both ways > (page_mapping is the correct place, flush_dcache_page is the more > efficient place), I suggest we leave it as is. Ok. I think your patch is fine as a quick fix for 2.6.22. I am a bit uneasy with that given that its in such a broadly used function while its only use is to enable flush_dcache_page to work. But we need the general issue taken care of after 2.6.22. > > A kmalloc slab object (even 64 byte) may be crossing a page boundary > > with a ARCH_KMALLOC_MINALIGN of 4 or 8. So I think that > > flush_dcache_range *must* be used rather than flush_dcache_page. > > Why???? All we require of flush_dcache_page is that it not oops on > the first page in the range: we don't need to change over to > flush_dcache_range for that. As explained about: There are corner cases in which it does not work. You seem to assume that flush_dcache_page can become a no op. That may not be true on platforms that need explicit cache flushing for a DMA engine to access a data structure. The above listed use suggests that the caller expects flushing to occur correctly. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
